Wavelength variable interference filter, optical module, and light analyzer

ABSTRACT

A wavelength variable interference filter includes: a first movable mirror disposed on a first substrate; a second movable mirror disposed so as to be opposed to the first movable mirror with a predetermined gap interposed therebetween; and an electrostatic actuator which varies the length of the gap between the mirrors. The first substrate has a first movable portion on which the first movable mirror is disposed, and a first linkage portion which holds the first movable portion in such a manner that the first movable portion can shift in the thickness direction of the substrate. The second substrate has a second movable portion on which the second movable mirror is disposed, and a second linkage portion which holds the second movable portion in such a manner that the second movable portion can shift in the thickness direction of the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation patent application of U.S. application Ser. No.13/219,925 filed Aug. 29, 2011, which claims priority to Japanese PatentApplication No. 2010-253956, filed Nov. 12, 2010 all of which areexpressly incorporated by reference herein in their entireties.

BACKGROUND

1. Technical Field

The present invention relates to a wavelength variable interferencefilter which selects light having a desired target wavelength fromincident light and releases the selected light, an optical module whichincludes this wavelength variable interference filter, and a lightanalyzer which includes this optical module.

2. Related Art

An optical filter (wavelength variable interference filter) whichincludes a pair of substrates each of which has a mirror disposed on asurface of the substrate on the side facing to the mirror of the othersubstrate is known (for example, see JP-A-2010-204457). This type ofwavelength variable interference filter causes multiple interference ofincident light between the pair of the mirrors, and allows onlytransmission of light having a particular wavelength and intensified bymultiple interference.

A wavelength variable interference filter disclosed in JP-A-2010-204457is provided with a first substrate and a second substrate disposed so asto be opposed to each other. An annular groove is formed on the surfaceof the first substrate on the side not facing to the second substrate sothat a cylindrical movable portion positioned at the center of the firstsubstrate and an annular diaphragm coaxial with the movable portion canbe defined by the groove. A pair of electrodes are disposed so as to beopposed to each other between the pair of the substrates. Mirrors areprovided both on the surface of the movable portion on the side facingto the second substrate and on the second substrate in such positions asto be opposed to each other. According to this structure, the diaphragmbends by the force of electrostatic attraction generated in response tovoltage applied to the pair of the electrodes, and shifts the movableportion to which the mirror is attached in the thickness direction ofthe substrate for control of the gap between the pair of the mirrors. Bythis mechanism, the wavelength variable interference filter can selectand transmit only light having the particular wavelength correspondingto the gap.

According to the wavelength variable interference filter disclosed inJP-A-2010-204457, the diaphragm is only provided on the first substrate.In this structure, reduction of the thickness of the diaphragm orenlargement of the area of the diaphragm in the plan view as viewed inthe thickness direction of the substrates is required when the gap isdesired to be narrowed by a large displacement amount of the movableportion. However, the diaphragm whose thickness is decreased or whosearea is increased easily moves, and therefore the mirror provided on themovable portion easily shifts as well. In this case, the gap between themirrors varies by external factors such as vibrations received from theoutside, which possibly makes it difficult to provide the desired gapbetween the mirrors in correspondence with the applied voltage.

SUMMARY

An advantage of some aspects of the invention is to provide a wavelengthvariable interference filter, an optical module, and a light analyzercapable of providing a desired gap with high accuracy while reducingvariations in the gap produced by external factors.

An aspect of the invention is directed to a wavelength variableinterference filter including: a first substrate; a second substratedisposed so as to be opposed to the first substrate; a first reflectionfilm provided on the surface of the first substrate on the side facingto the second substrate; a second reflection film provided on the secondsubstrate and disposed so as to be opposed to the first reflection filmwith a predetermined gap interposed therebetween; and a gap varying unitwhich changes the length of the gap between the first reflection filmand the second reflection film. The first substrate has a first movableportion on which the first reflection film is disposed, and a firstlinkage portion which holds the first movable portion in such a mannerthat the first movable portion can shift in the thickness direction ofthe first substrate. The second substrate has a second movable portionon which the second reflection film is disposed, and a second linkageportion which holds the second movable portion in such a manner that thesecond movable portion can shift in the thickness direction of thesecond substrate. The gap varying unit varies the length of the gap byshifting the first movable portion and the second movable portionrelative to each other.

Generally, for shifting a movable portion by a predetermineddisplacement amount, decrease in the thickness of a diaphragm orincrease in the area of the diaphragm in the plan view is required asexplained above. In this case, variations in the gap may be produced dueto external factors such as vibrations. According to the structure ofthis aspect of the invention, however, the first substrate and thesecond substrate have the first and second movable portions and thefirst and second linkage portions, respectively. Thus, when externalfactors such as vibrations are given to the first and second substrates,the first and second movable portions shift in the same direction,thereby reducing the variations in the gap length. Moreover, therespective linkage portions bend in directions closer to each other bythe function of the gap varying unit, and the respective movableportions shift in directions closer to each other accordingly. In thiscase, the sum of the displacement amounts of the first movable portionand the second movable portion is only required to be equivalent to thedisplacement amount in the structure of the related art, which reduceseach of the displacement amounts of the movable portions to a volumesmaller than the corresponding amount of the structure of the relatedart. Thus, the thickness and the area of each of the linkage portionscan be made larger than the corresponding thickness and area in thediaphragm of the related art, which decreases variations in the gapproduced by the external factors. Accordingly, the gap can be accuratelyset at a desired length in accordance with applied voltage.

It is preferable that the wavelength variable interference filter of theaspect of the invention has the following structures. The firstsubstrate has a first displacement unit provided with the first movableportion and the first linkage portion. The second substrate has a seconddisplacement unit provided with the second movable portion and thesecond linkage portion. The first displacement unit and the seconddisplacement unit are made of the same material and have the same shape.

According to this structure, the first displacement unit of the firstsubstrate and the second displacement unit of the second substrate aremade of the same material and have the same shape. Thus, the bendvolumes of the first linkage portion and the second linkage portionproduced when external factors are given thereto are equalized, wherebythe displacement amounts of the first movable portion and the secondmovable portion become equivalent. In this case, the respective movableportions shift by the same displacement amount and in the same directionwhen the external factors such as vibrations are given thereto.Accordingly, variations in the gap can be further reduced.

It is preferable that the wavelength variable interference filter of theaspect of the invention has the following structures. The firstdisplacement unit has a linearly symmetric shape with respect to asymmetry axis corresponding to a line which passes through the centerline of the first linkage portion in the thickness direction of thefirst substrate and extending in parallel with the surface of the firstreflection film in the cross-sectional view taken in the thicknessdirection of the first substrate. The second displacement unit has alinearly symmetric shape with respect to a symmetry axis correspondingto a line which passes through the center line of the second linkageportion in the thickness direction of the second substrate and extendingin parallel with the surface of the second reflection film in thecross-sectional view taken in the thickness direction of the secondsubstrate.

According to this structure, each of the displacement units has thelinearly symmetric shape with respect to the symmetry axis correspondingto the line which passes through the center line of the linkage portionin the thickness direction of the substrate and extending in parallelwith the reflection film.

In the case where the displacement units do not have a linearlysymmetric structure, when the displacement units vibrate in the surfacedirections of the substrates due to external factors such as externalvibrations, each of the displacement units receives a force in itssurface direction. The forces acting on the displacement units becomeunbalanced, which varies the gap between the reflection films providedon the respective movable portions. According to the structure of thisaspect of the invention, however, each of the displacement units has alinearly symmetric shape which provides a good balance of the forcesacting on the displacement units in the surface directions. Thus,variations in the gap can be reduced even when the displacement unitsvibrate in the surface directions of the substrates.

Accordingly, the wavelength variable interference filter in this aspectof the invention can reduce variations in the gap even when externalfactors such as vibrations in the thickness directions or in the surfacedirections of the substrates are given to the wavelength variableinterference filter.

It is preferable that the first substrate and the second substrate ofthe wavelength variable interference filter of the aspect of theinvention are made of the same material and have the same shape.

According to this structure, the respective substrates are made of thesame material and have the same shape. In this case, the variations inthe gap can be reduced. Moreover, the manufacturing steps for therespective substrates can be equalized, which simplifies themanufacturing steps.

It is preferable that the wavelength variable interference filter of theaspect of the invention has the following structures. The gap varyingunit has a first electrode provided on the surface of the firstsubstrate facing to the second substrate, and a second electrodeprovided on the second substrate in such a position as to be opposed tothe first electrode. A first bend prevention film is provided on thesurface of the first substrate opposite to the surface where the firstelectrode is disposed as a bend prevention film made of the samematerial as that of the first electrode, and on the surface of thesecond substrate opposite to the surface where the second electrode isdisposed as a bend prevention film made of the same material as that ofthe second electrode. A second bend prevention film is provided on thesurface of the first substrate opposite to the surface where the firstreflection film is disposed as a bend prevention film made of the samematerial as that of the first reflection film, and on the surface of thesecond substrate opposite to the surface where the second reflectionfilm is disposed as a bend prevention film made of the same material asthat of the second reflection film.

Generally, the coefficient of linear expansion which is dependent on thetemperatures of the reflection films and the electrodes provided on thesubstrates varies when the environment temperature changes. In thiscase, the internal stresses of the reflection films and the electrodesvary, and may bend the substrates due to the temperature change.

According to the structure of this aspect of the invention, the firstbend prevention film made of the same material as that of the electrodeis provided on each surface of the substrates on the side opposite tothe surface where the electrode is disposed, and the second bendprevention film made of the same material as that of the reflection filmis provided on each surface of the substrates on the side opposite tothe surface where the reflection film is disposed. In this case, theinternal stresses of the electrodes and the reflection films acting onthe substrates are balanced against the forces of the first and secondbend prevention films acting on the substrates when the environmenttemperature changes. Thus, the respective substrates do not bend, andparallelism between the first and second reflection films is obtained.Accordingly, the resolution of the wavelength variable interferencefilter increases.

Another aspect of the invention is directed to an optical moduleincluding: the wavelength variable interference filter described above;and a light receiving unit which receives test target light transmittedby the wavelength variable interference filter.

According to this aspect of the invention, variations in the gapproduced by external factors such as vibrations can be reduced similarlyto the above aspect of the invention. Thus, the gap of the wavelengthvariable interference filter can be set at a desired length inaccordance with applied voltage with high accuracy. Accordingly, theoptical module can perform highly accurate measurement by using thelight receiving unit.

Still another aspect of the invention is directed to a light analyzerincluding: the optical module described above; and an analyzing unitwhich analyzes light characteristics of the test target light based onlight received by the light receiving unit of the optical module.

The light analyzer according to this aspect of the invention includesthe optical module which has the wavelength variable interference filterdescribed above. Thus, the light analyzer can perform highly accuratemeasurement, and thus can measure accurate spectral characteristicsbased on the measurement result.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a block diagram showing the general structure of a colorimeteraccording to a first embodiment of the invention.

FIG. 2 is a plan view illustrating the general structure of an etalonaccording to the first embodiment.

FIG. 3 is a cross-sectional view illustrating the general structure ofthe etalon according to the first embodiment.

FIGS. 4A through 4E show manufacturing steps of each substrate of theetalon according to the first embodiment.

FIG. 5 is a plan view illustrating the general structure of an etalonaccording to a second embodiment of the invention.

FIG. 6 is a cross-sectional view illustrating the general structure ofthe etalon according to the second embodiment.

FIGS. 7A through 7F show manufacturing steps of each substrate of theetalon according to the second embodiment.

FIG. 8 is a cross-sectional view of an etalon according to a modifiedexample of the invention.

FIG. 9 is a plan view of an etalon according to another modified exampleof the invention.

FIG. 10 is a plan view of an etalon according to a further modifiedexample of the invention.

FIG. 11 is a cross-sectional view of an etalon according to a stillfurther modified example of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS First Embodiment

A first embodiment according to the invention is hereinafter describedwith reference to the drawings.

1. General Structure of Colorimeter

FIG. 1 is a block diagram showing the general structure of a colorimeter1 (light analyzer) according to the first embodiment.

As illustrated in FIG. 1, the colorimeter 1 includes a light sourcedevice 2 which emits light toward a test target A, a colorimetric sensor3 (optical module), and a control device 4 which controls the overalloperation of the colorimeter 1. The colorimeter 1 is a system whichanalyzes and measures the chromaticity of test target light, that is,the color of the test target A based on a detection signal outputtedfrom the colorimetric sensor 3 having received test target light emittedfrom the light source device 2 and reflected by the test target A.

2. Structure of Light Source Device

The light source device 2 includes a light source 21 and a plurality oflenses 22 (only one of these is shown in FIG. 1), and emits white lighttoward the test target A. The plural lenses 22 may include a collimatorlens. In this case, the light source device 2 collimates the white lightemitted from the light source 21 by the function of the collimator lens,and emits the collimated light from a not-shown projection lens towardthe test target A. While the colorimeter 1 provided with the lightsource device 2 is discussed in this embodiment, the light source device2 may be eliminated when the test target A is a light emission unit suchas a liquid crystal panel.

3. Structure of Colorimetric Sensor

As illustrated in FIG. 1, the colorimetric sensor 3 includes an etalon 5(wavelength variable interference filter), a light receiving element 31(light receiving unit) which receives light having passed through theetalon 5, and a voltage control unit 6 which varies the wavelength oflight that can pass through the etalon 5. The colorimetric sensor 3 hasa not-shown entrance optical lens disposed at the position opposed tothe etalon 5 to introduce light reflected by the test target A (testtarget light) into the etalon 5. The colorimetric sensor 3 divides lighthaving a predetermined wavelength from the test target light receivedfrom the entrance optical lens by using the talon 5, and receives thedivided light via the light receiving element 31.

The light receiving element 31 constituted by a plurality ofphoto-electric switching elements produces electric signalscorresponding to the received amounts of lights. The light receivingelement 31 is connected with the control device 4 to output thegenerated electric signals to the control device 4 as light receptionsignals.

3-1. Structure of Etalon

FIG. 2 is a plan view illustrating the general structure of the etalon5. FIG. 3 is a cross-sectional view of the etalon 5 taken along a lineIII-III in FIG. 2 as viewed in the direction of arrows. In FIG. 1, thetest target light enters the etalon 5 from below as viewed in thefigure. In FIG. 3, however, the test target light enters the etalon 5from above as viewed in the figure.

As illustrated in FIG. 2, the etalon 5 is a plate-shaped opticalcomponent having a square shape in the plan view, and has sides each ofwhich is 10 mm long, for example. As illustrated in FIG. 3, the etalon 5has a first substrate 51 and a second substrate 52 disposed in thisorder as viewed from the entrance side of the test target light. Thesesubstrates 51 and 52 are bonded to each other with bonding layers 53interposed therebetween by cold activation bonding or siloxane bondingwhich uses plasma polymeric film, for example, to be combined into onebody. The first substrate 51 and the second substrate 52 have the sameshape, and are disposed linearly symmetric with respect to the centeraxis corresponding to the bonding layers 53 in the cross-sectional viewin FIG. 3. Each of the two substrates 51 and 52 is made of glass such assoda glass, crystal glass, quartz glass, lead glass, potassium glass,borosilicate glass, and non-alkali glass, or crystal, for example.

A first movable mirror 56 (first reflection film) and a second movablemirror 57 (second reflection film) are provided between the firstsubstrate 51 and the second substrate 52. The first movable mirror 56 isfixed to a surface (first movable surface 515A described later) of thefirst substrate 51 on the side facing to the second substrate 52, whilethe second movable mirror 57 is fixed to a surface (second movablesurface 525A described later) of the second substrate 52 on the sidefacing to the first substrate 51. The first and second movable mirrors56 and 57 are disposed so as to be opposed to each other with a gap Gleft between the mirrors 56 and 57.

An electrostatic actuator 54 is further provided between the firstsubstrate 51 and the second substrate 52 to control the length of thegap G between the movable mirrors 56 and 57.

3-1-1. Structure of First Substrate

The first substrate 51 is manufactured from a glass material which is200 μm thick, for example, by etching. A first displacement unit 511having a circular shape around the substrate center in the plan view asviewed in the thickness direction of the etalon 5 as illustrated in FIG.2 (hereinafter referred to as “etalon plan view”) is formed on the firstsubstrate 51. The first displacement unit 511 is coaxial with acylindrical first movable portion 512, and has a first linkage portion513 which is annular in the etalon plan view and holds the first movableportion 512 in such a manner that the first movable portion 512 canshift in the thickness direction of the first substrate 51.

The first displacement unit 511 is defined by a groove formed on theplate-shaped glass material of the first substrate 51 by etching. Morespecifically, the first displacement unit 511 is defined by a firstannular groove 513A having an annular shape and formed by etching on thelight entrance surface of the first substrate 51 on the side not facingto the second substrate 52 as a groove along which the first linkageportion 513 is produced.

A first circular groove 514 which has a circular shape around thesubstrate center in the etalon plan view is formed by etching on thesurface of the first displacement unit 511 on the side facing to thesecond substrate 52.

As explained above, the first and second substrates 51 and 52 are madeof the same material and have the same shape. Thus, the firstdisplacement unit 511 thus constructed is made of the same material andhas the same shape as those of a second displacement unit 521 of thesecond substrate 52 (described later).

The first movable portion 512 has a larger thickness than that of thefirst linkage portion 513. The first movable portion 512 has a secondcircular groove 515 which has a circular shape around the substratecenter in the etalon plan view. The second circular groove 515 is formedby etching on the bottom of the first circular groove 514 correspondingto the surface of the first movable portion 512 on the side facing tothe second substrate 52. The second circular groove 515 is coaxial withthe first circular groove 514, and has a smaller diameter than that ofthe first circular groove 514. The first movable mirror 56 ismanufactured from a circular dielectric multilayer film made ofTiO₂—SiO₂ family and having a diameter of about 3 mm, and is fixed tothe first movable surface 515A corresponding to the bottom of the secondcircular groove 515.

According to this embodiment, the first movable mirror 56 is a mirrorformed by the dielectric multilayer film of TiO₂—SiO₂ family. However,the first movable mirror 56 may be constituted by a monolayer mirrormade of Ag alloy which covers the entire range of visible light as thewavelength range dividable by the mirror.

The first linkage portion 513 is a diaphragm surrounding the peripheryof the first movable portion 512, and has a thickness of 50 μm, forexample. A first electrode 541 having an annular shape in the etalonplan view is provided on the first linkage portion 513. The firstelectrode 541 is disposed on a first electrode fixing surface 514Acorresponding to the bottom of the first circular groove 514 and opposedto the second substrate 52.

The material of the first electrode 541 is not specifically limited aslong as it has conductivity and can generate an electrostatic attractiveforce between the first electrode 541 and a second electrode 542(described later) of the second substrate 52 in response to voltageapplied between the first electrode 541 and the second electrode 542. Inthis embodiment, the first electrode 541 is made of ITO (indium tinoxide), but may be made of other materials such as an Au/Cr metallaminated body.

A not-shown insulation film is provided on the upper surface of thefirst electrode 541 to prevent leakage caused by discharge between thefirst electrode 541 and the second electrode 542 or for other reasons.This insulation film is constituted by SiO₂ or TEOS (tetraethoxysilane),for example. It is particularly preferable that the insulation film ismade of SiO₂ having optical characteristics similar to those of theglass substrate forming the first substrate 51. When the insulation filmis constituted by SiO₂, reflection of light between the first substrate51 and the insulation film or other problems do not occur. Thus, afterformation of the first electrode 541 on the first substrate 51, theentire surface of the first substrate 51 on the side facing to thesecond substrate 52 can be coated with the insulation film made of SiO₂.

A first electrode extension portion 541L extends from a part of theouter circumference of the first electrode 541 toward the lower left ofthe etalon 5 in the etalon plan view shown in FIG. 2. A first electrodepad 541P provided at the end of the first electrode extension portion541L is connected with the voltage control unit 6 (see FIG. 1).

During operation of the electrostatic actuator 54, voltage is applied tothe first electrode pad 541P from the voltage control unit 6 (see FIG.1).

The portion of the first substrate 51 where the first circular groove514 is not formed corresponds to a bonding surface 51A of the firstsubstrate 51. As illustrated in FIGS. 2 and 3, the bonding layer 53 isprovided in the form of film on the bonding surface 51A. The bondinglayer 53 is constituted by a plasma polymeric film chiefly includingpolyorganosiloxane, for example.

3-1-2. Structure of Second Substrate

As noted above, the second substrate 52 has a shape same as that of thefirst substrate 51. Thus, the structure of the second substrate 52 isherein explained only briefly.

The second substrate 52 is manufactured from a glass material which is200 μm thick, for example, by etching similarly to the first substrate51. A second displacement unit 521 having a circular shape in the etalonplan view is provided on the second substrate 52. As illustrated in FIG.2, the second displacement unit 521 has a cylindrical second movableportion 522, and a second linkage portion 523 which holds the secondmovable portion 522 in such a manner that the second movable portion 522can shift in the thickness direction of the second substrate 52.

According to this structure, the substrates 51 and 52 have the linkageportions 513 and 523, respectively. Thus, the movable portions 512 and522 of the substrates 51 and 52 shift closer to each other when anelectrostatic attractive force is generated between the first electrode541 and the second electrode 542 (described later).

A first annular groove 523A having an annular shape and defining thesecond linkage portion 523 is formed by etching on the surface of thesecond displacement unit 521 on the side not facing to the firstsubstrate 51.

In addition, a third circular groove 524 having a circular shape aroundthe substrate center in the etalon plan view is formed by etching on thesurface of the second displacement unit 521 on the side facing to thefirst substrate 51.

The second movable portion 522 has a fourth circular groove 525 whichhas a circular shape around the substrate center in the etalon planview. The fourth circular groove 525 is formed by etching on the bottomof the third circular groove 524 corresponding to the surface of thesecond movable portion 522 on the side facing to the first substrate 51.The fourth circular groove 525 is coaxial with the third circular groove524, and has a smaller diameter than that of the third circular groove524.

The second movable surface 525A corresponding to the bottom of thefourth circular groove 525 and extending in parallel with the firstmovable surface 515A is a surface to which the second movable mirror 57constructed the same as the first movable mirror 56 is fixed.

The second linkage portion 523 is disposed so as to be opposed to thefirst substrate 51. The second electrode 542 having an annular shape inthe etalon plan view is provided on a second electrode fixing surface524A corresponding to the bottom surface of the third circular groove524. The second electrode 542 is positioned so as to be opposed to thefirst electrode 541 with a predetermined gap interposed therebetween,and is constructed the same as the first electrode 541. Theelectrostatic actuator 54 functioning as a gap varying unit in theappended claims is constituted by the second electrode 542 and the firstelectrode 541 described above.

A second electrode extension portion 542L extends from a part of theouter circumference of the second electrode 542 toward the upper rightof the etalon 5 in the etalon plan view shown in FIG. 2. A secondelectrode pad 542P provided at the end of the second electrode extensionportion 542L is connected with the voltage control unit 6 similarly tothe first electrode pad 541P.

During operation of the electrostatic actuator 54, voltage is applied tothe second electrode pad 542P from the voltage control unit 6 (see FIG.1).

The portion of the second substrate 52 on the side facing to the firstsubstrate 51 as the area where the second circular groove 524 is notformed corresponds to a bonding surface 52A of the second substrate 52.The bonding layer 53 chiefly including polyorganosiloxane is provided onthe bonding surface 52A similarly to the bonding surface 51A of thefirst substrate 51.

According to the etalon 5 having the first substrate 51 and the secondsubstrate 52 thus constructed, the first linkage portion 513 and thesecond linkage portion 523 are bended when predetermined voltage isapplied to the electrostatic actuator 54. As a result, the first movableportion 512 and the second movable portion 522 shift relative to eachother. The sum of the displacement amounts of the respective movableportions 512 and 522 determine the length of the gap G between themirrors.

3-2. Structure of Voltage Control Unit

The voltage control unit 6 controls voltage applied to the firstelectrode 541 and the second electrode 542 of the electrostatic actuator54 in response to a control signal received from the control device 4.

4. Structure of Control Device

The control device 4 controls the overall operation of the colorimeter1. The control device 4 is constituted by a general-purpose personalcomputer, a mobile information terminal, a computer used exclusively forcolorimetry, for example.

As illustrated in FIG. 1, the control device 4 includes a light sourcecontrol unit 41, a colorimetric sensor control unit 42, and acolorimetric processing unit 43 (analyzing unit).

The light source control unit 41 is connected with the light sourcedevice 2. The light source control unit 41 outputs a predeterminedcontrol signal to the light source device 2 based on a setting inputfrom a user, for example, and allows the light source device 2 to emitwhite light having predetermined brightness.

The colorimetric sensor control unit 42 is connected with thecolorimetric sensor 3. The colorimetric sensor control unit 42determines the wavelength of light to be received by the colorimetricsensor 3 based on a setting input from the user, for example, andoutputs a control signal for allowing the colorimetric sensor 3 todetect the amount of light having the determined wavelength. Based onthe control signal, the voltage control unit 6 of the colorimetricsensor 3 determines voltage to be applied to the electrostatic actuator54 such that only the light having the desired wavelength selected bythe user can be transmitted at the determined voltage.

The colorimetric processing unit 43 varies the gap between the mirrorsof the etalon 5 and changes the wavelength of light which can passthrough the etalon 5 by controlling the colorimetric sensor control unit42. The colorimetric processing unit 43 acquires the information aboutthe amount of light having passed through the etalon 5 based on thelight reception signal received from the light receiving element 31. Thecolorimetric processing unit 43 calculates the chromaticity of the lightreflected by the test target A and having the desired wavelength basedon the amount of the light obtained in this manner.

5. Etalon Manufacturing Method

A method of manufacturing the etalon 5 is now explained with referenceto FIG. 4A through 4E.

For manufacturing the etalon 5, the first substrate 51 and the secondsubstrate 52 are separately produced, and affixed to each other aftercompletion of each of the substrates 51 and 52. Since the steps formanufacturing each of the substrates 51 and 52 are the same, only themanufacturing steps of the first substrate 51 are herein described.

A quartz glass substrate which is 200 μm thick is prepared as a materialof the first substrate 51. Both surfaces of the glass substrate areprecision-ground until a surface roughness Ra of the glass substratebecomes 1 nm or smaller. As illustrated in FIG. 4A, a resist 61 isapplied to the upper surface and the lower surface of the firstsubstrate 51.

The resist 61 applied to the surfaces is exposed and developed byphotolithography. The areas where the first linkage portion 513 (firstannular groove 513A) and the first circular groove 514 (first electrodefixing surface 514A) are formed are patterned. The first substrate 51 issoaked in etchant such as HF, and wet-etched until the upper surface andthe lower surface of the first substrate 51 have desired depths asillustrated in FIG. 4B. The relationship between the depth of theetching and the time of the soakage of the substrate in the etchant isdetermined beforehand. Thus, the first substrate 51 is soaked in theetchant for a predetermined time to form the first annular groove 513Aand the first circular groove 514.

Another resist 62 is applied to the bottom of the first circular groove514. The applied resist 62 is exposed and developed by photolithography.The area where the second circular groove 515 (first movable surface515A) is formed is patterned. The lower surface of the first substrate51 is wet-etched to a desired depth to form the second circular groove515 as illustrated in FIG. 4C.

The resists 61 and 62 are removed to produce the first linkage portion513 which is 50 μm thick, the first movable portion 512, the firstelectrode fixing surface 514A, and the first movable surface 515A.

A resist (lift off pattern) is applied to the area of the lower surfaceof the first substrate 51 other than the position of the first electrode541. An ITO layer is formed by sputtering, and the resist is removed. Asa result, the first electrode 541 is produced on the first electrodefixing surface 514A as illustrated in FIG. 4D.

A resist (lift off pattern) is applied to the area of the first movablesurface 515A other than the position of the first movable mirror 56. Athin film of TiO₂—SiO₂ family is formed by sputtering, and the resist isremoved. As a result, the circular first movable mirror 56 having adiameter of about 3 mm is produced on the first movable surface 515A asillustrated in FIG. 4E.

Manufacture of the first substrate 51 is now completed.

The second substrate 52 is produced by the same manufacturing steps asthose of the first substrate 51, and thus is manufactured simultaneouslywith the manufacture of the first substrate 51. The second substrate 52may be produced by repeating the manufacturing steps of the firstsubstrate 51.

The first substrate 51 and the second substrate 52 thus produced arebonded to each other. More specifically, O₂ plasma processing or UVprocessing is performed for giving activation energy to each of theplasma polymeric films constituting the bonding layers 53 provided onthe bonding surfaces 51A and 52A of the substrates 51 and 52. The O₂plasma processing is executed for 30 seconds under the condition of theO₂ flow amount of 30 cc/min., the pressure of 27 Pa, and the RF power of200 W. The UV processing is executed for 3 minutes by using excimer UV(wavelength: 172 nm) as the UV light source. After the activation energyis given to the plasma polymeric films, the two substrates 51 and 52 arealigned with each other. Then, the bonding surfaces 51A and 52A areoverlapped with each other via the bonding layers interposedtherebetween, and a load is applied to the overlapped bonding surfaces51A and 52A to bond the substrates 51 and 52.

The manufacture of the etalon 5 is now finished.

6. Advantages of First Embodiment

According to the etalon 5 in the first embodiment, the followingadvantages can be offered.

(1) The first substrate 51 and the second substrate 52 have the movableportions 512 and 522 and the linkage portions 513 and 523. When voltageis applied to the electrodes 541 and 542, the linkage portions 513 and523 are bended nearer to each other, which shifts the movable portions512 and 522 closer to each other accordingly. In this case, the sum ofthe displacement amounts of the first movable portion 512 and the secondmovable portion 522 is only required to be equivalent to thedisplacement amount of a movable portion in the structure of the relatedart described above which has the movable portion only on one of thesubstrates. That is, each of the displacement amounts of the movableportions 512 and 522 is only required to be equivalent to the half ofthe displacement amount in the related art. Thus, the variations in thegap caused by external factors can be reduced without decreasing thethickness and the area of each of the linkage portions 513 and 523.Accordingly, the gap can be set at a desired length corresponding to theapplied voltage with high accuracy.

(2) The respective substrates 51 and 52 are made of the same materialand have the same shape. Thus, the bending volumes of the first linkageportion 513 and the second linkage portion 523 produced when externalfactors are given thereto become equivalent, which equalizes thedisplacement amounts of the first movable portion 512 and the secondmovable portion 522. In this case, the respective movable portions 512and 522 of the substrates 51 and 52 shift by the same shift amount inthe same direction when the movable portions 512 and 522 receiveexternal factors such as vibrations described above. Accordingly, thevariations in the gap can be further reduced. Moreover, the substrates51 and 52 can be produced by the same manufacturing steps, whichsimplifies the process of manufacture.

(3) The substrates 51 and 52 have the first movable portion 512 and thesecond movable portion 522. In this case, the desired length of the gapis determined by the sum of the displacement amounts of the firstmovable portion 512 and the second movable portion 522. Thus, only thehalf of the displacement amount of the movable portion in therelated-art structure which has the movable portion only on one of thesubstrates is required for each of the movable portions 512 and 522.Accordingly, the voltage required to be applied to the electrostaticactuator 54 for shifting the movable portions 512 and 522 can bedecreased, which contributes to power saving.

For achieving power saving, reduction of the thickness of the linkageportion is expected to be an effective solution in case of the structurewhich has the movable portion only on one of the substrates, forexample. In this case, however, variations in the gap may be caused bythe external factors described above. According to this embodiment,power saving can be achieved without decreasing the thickness and thelike of the linkage portion.

Second Embodiment

A second embodiment according to the invention is hereinafter describedwith reference to FIGS. 5 and 6.

An etalon 5A in this embodiment is constructed similarly to the etalon 5in the first embodiment. However, the etalon 5A is different from theetalon 5 in that the linkage portions 513 and 523 of the substrates 51and 52 are disposed at the centers of the substrates 51 and 52 in thecross-sectional view in FIG. 6, and that an anti-reflection film 58 anda dummy electrode 59 are provided on each of the substrates 51 and 52.

In this embodiment, the components and parts corresponding to the samecomponents and parts in the first embodiment are given the samereference numbers, and the same explanation is not repeated.

The etalon 5A includes the first substrate 51 and the second substratehaving the same shape similarly to the first embodiment. Thus, only thestructure of the first substrate 51 is discussed herein, and theexplanation of the structure of the second substrate 52 is not repeated.

The first displacement unit 511 of the first substrate 51 includes thecylindrical first movable portion 512 to which the first movable mirror56 is fixed, the first linkage portion 513 having an annular shape inthe etalon plan view, and the first electrode fixing portion 516 havingan annular shape in the etalon plan view and disposed between the firstmovable portion 512 and the first linkage portion 513 as a surface towhich the first electrode 541 is fixed.

The first movable portion 512 has a thickness larger than the thicknessof the first linkage portion 513 and smaller than the thickness of thefirst electrode fixing portion 516. The first movable portion 512 formedat the center of the substrate in the substrate thickness direction inthe cross-sectional view in FIG. 6 is defined by circular grooves 517having the same shape and the same groove depth and formed by etching onthe upper surface and the lower surface of the first substrate 51. Thefirst movable mirror 56 is provided on the bottom of the circular groove517 on the side facing to the second substrate 52, while theanti-reflection film 58 (second bend prevention film) made of the samematerial as that of the first movable mirror 56 is provided on thebottom of the circular groove 517 on the side corresponding to the lightentrance surface of the first substrate 51.

The anti-reflection film 58 having a function of preventing reflectionof received light and increasing transmission light is disposed at theposition overlapping with the first movable mirror 56 in the etalon planview. The anti-reflection film 58 reduces a bend of the first substrate51 produced when the stress acting in the surface direction of the firstmovable mirror 56 varies due to the change of the environmenttemperature. More specifically, when the environment temperaturechanges, the coefficient of linear expansion and the like of the firstmovable mirror 56 vary. In this case, the internal stress of the firstmovable mirror 56 varies accordingly and produces a bend of the firstsubstrate 51. According to this structure, the anti-reflection film 58made of the same material as that of the first movable mirror and formedsuch that the internal stresses of the anti-reflection film 58 and thefirst movable mirror 56 can be equivalent is equipped. In this case, thecoefficient of linear expansion and the like of the anti-reflection film58 similarly vary when the environment temperature changes, in whichcondition the internal stress of the anti-reflection film 58 variesaccordingly. Thus, when the anti-reflection film 58 is formed such thatthe internal stress of the anti-reflection film 58 acts in the directionopposite to the direction in which the internal stress of the firstmovable mirror 56 acts, the bending moment produced by the internalstress of the first movable mirror 56 and acting on the first substrate51 can be balanced against the bending moment produced by the internalstress of the anti-reflection film 58 and acting on the first substrate51. By this mechanism, reduction of the bend of the first substrate 51is realized.

The first linkage portion 513 is disposed at the center in the thicknessdirection of the first substrate 51 in the cross-sectional view in FIG.6. In this structure, a second annular groove 513B having an annularshape and having the same shape and groove depth as those of the firstannular groove 513A is formed on the surface of the first substrate 51on the side facing to the second substrate 52 as well as the firstannular groove 513A provided on the light entrance surface of the firstsubstrate 51.

The upper and lower surfaces of the first substrate 51 are etched toproduce the first electrode fixing portion 516 having a predeterminedthickness and defined by the circular grooves 517 and the annulargrooves 513A and 513B. The first electrode fixing portion 516 has athickness larger than the thickness of the first movable portion 512 andthan the thickness of the first linkage portion 513, and is disposed atthe center in the substrate thickness direction in the cross-sectionalview in FIG. 6. Therefore, the gap length between the first electrode541 and the second electrode 542 is smaller than the gap length betweenthe first movable mirror 56 and the second movable mirror 57 in thisembodiment similarly to the first embodiment.

The ring-shaped first electrode 541 is provided on the surface of thefirst electrode fixing portion 516 on the side facing to the secondsubstrate 52, and the dummy electrode 59 (first bend prevention film)made of the same material and having the same shape as those of thefirst electrode 541 is provided on the light entrance surface of thefirst electrode fixing portion 516. That is, the dummy electrode 59 isoverlapped on the first electrode 541 in the etalon plan view.

The dummy electrode 59 functions similarly to the anti-reflection film58, and reduces the bend of the first substrate 51 produced byvariations in the coefficient of linear expansion and the like of thefirst electrode 541 due to the change of the environment temperature.The specific operation of the dummy electrode 59 is similar to that ofthe anti-reflection film 58, and therefore is not particularly explainedherein.

As obvious from the above description, the first movable portion 512,the first linkage portion 513, and the first electrode fixing portion516 of the first substrate 51 in this embodiment are positioned at thecenter in the substrate thickness direction. The first displacement unit511 has a linearly symmetric structure with respect to a symmetric axiscorresponding to a line which passes through the center line of thefirst linkage portion 513 in the substrate thickness direction andextending in parallel with the surfaces of the movable mirrors 56 and57. The second displacement unit 521 of the second substrate 52 isshaped the same as the first displacement unit 511, and thus has alinearly symmetric structure with respect to a symmetric axiscorresponding to a line which passes through the center of the secondlinkage portion 523 in the thickness direction of the second substrate52 and extending in parallel with the surfaces of the movable mirrors 56and 57.

The method of manufacturing the etalon 5A is now explained withreference to FIGS. 7A through 7F. Similarly to the first embodiment,only the manufacturing steps of the first substrate 51 are hereindescribed, and the explanation of the manufacturing steps of the secondsubstrate 52 is not repeated.

A quartz glass substrate is prepared as a material of the firstsubstrate 51. Both surfaces of the glass substrate are precision-grounduntil the surface roughness Ra of the glass substrate becomes 1 nm orsmaller. As illustrated in FIG. 7A, the resist 61 is applied to theupper surface and the lower surface of the first substrate 51.

The resist 61 applied to the surfaces is exposed and developed byphotolithography. The area where the first movable portion 512 is formedis patterned. The first substrate 51 is soaked in etchant such as HF,and the upper surface and the lower surface of the first substrate 51are wet-etched as illustrated in FIG. 7B. As a result, a circular groove517A having a depth smaller than the depth of the circular groove 517 isformed on each of the upper surface and the lower surface of the firstsubstrate 51.

The applied resist 61 is further exposed and developed byphotolithography. The area where the first electrode fixing portion 516is formed is patterned. The circular grooves 517A formed on the upperand the lower surfaces of the first substrate 51 are wet-etched to adesired depth to produce the circular grooves 517 having the desireddepth and defining the first movable portion 512. Moreover, the circulargrooves 518 each of which has a diameter larger than that of thecircular groove 517 and is coaxial with the circular groove 517 areformed as grooves defining the first electrode fixing portion 516.

The applied resist 61 is further exposed and developed byphotolithography. The area where the first linkage portion 513 (annulargrooves 513A and 513B) is formed is patterned. As illustrated in FIG.7D, the resist 62 is also applied to the first movable portion 512 andthe first electrode fixing portion 516. The upper surface and the lowersurface of the first substrate 51 are wet-etched to produce the annulargrooves 513A and 513B having the desired depths and defining the firstlinkage portion 513 which is 50 μm thick as illustrated in FIG. 7D.

The resists 61 and 62 are removed to obtain the first linkage portion513, the first electrode fixing portion 516, and the first movableportion 512.

A resist (lift off pattern) is applied to the upper surface of the firstsubstrate 51 in the area other than the position of the dummy electrode59, and to the lower surface of the first substrate 51 in the area otherthan the position of the first electrode 541. An ITO layer is formed bysputtering, and the resist is removed. By this step, the first electrode541 and the dummy electrode 59 are formed on the first electrode fixingportion 516 as illustrated in FIG. 7E.

A resist (lift off pattern) is further applied to the upper surface ofthe first movable portion 512 in the area other than the position of theanti-reflection film 58, and to the lower surface of the first movableportion 512 in the area other than the position of the first movablemirror 56. Then, a thin film made of TiO₂—SiO₂ family is formed bysputtering, and the resist is removed. By this step, the first movablemirror 56 and the anti-reflection film 58 each of which has a circularshape and a diameter of about 3 mm are produced on the first movableportion 512.

The manufacture of the first substrate 51 is now completed.

The second substrate 52 is produced by the manufacturing steps same asthose of the first substrate 51 described above.

The respective substrates 51 and 52 are bonded to each other in a mannersimilar to that of the first embodiment to obtain the etalon 5A.

According to the etalon 5A in the second embodiment, the followingadvantages can be offered as well as the advantages (1) through (3)provided in the first embodiment.

According to this embodiment, the respective substrates 51 and 52 arelinearly symmetric with respect to the symmetric axis corresponding tothe line which passes through the center of the linkage portions 513 and523 in the substrate thickness direction and extends in parallel withthe surfaces of the movable mirrors 56 and 57 in the cross-sectionalview.

When external factors such as vibrations are given to the displacementunits 511 and 521, these units 511 and 521 vibrate in the surfacedirections of the substrates and receive forces in the surfacedirections. When the displacement units 511 and 521 are not linearlysymmetric, the forces acting on the respective units 511 and 521 becomeunbalanced, and change the gap between the mirrors provided on themovable portions 512 and 522. According to this embodiment, however, therespective displacement units 511 and 521 are linearly symmetric, andthe forces acting on the displacement units 511 and 521 can bewell-balanced in the surface directions. Thus, even when thedisplacement units 511 and 521 vibrate in the surface directions of thesubstrates 51 and 52, variations in the gap can be reduced.

Accordingly, the change of the gap length can be reduced in thisembodiment even when the substrates 51 and 52 vibrate in the thicknessdirections or the surface directions due to external factors given tothe substrates 51 and 52.

When the environment temperature changes, the internal stresses of themovable mirrors 56 and 57 and of the electrodes 541 and 542 formed onthe substrates 51 and 52 vary as explained above. In this case, thesubstrates 51 and 52 may be bended in accordance with the variations inthe internal stresses. According to this embodiment, the dummy electrode59 made of the same material and having the same shape as those of theelectrodes 541 and 542 is provided on each of the surfaces of thesubstrates 51 and 52 on the side opposite to the surface where theelectrodes 541 and 542 are formed, and the anti-reflection film 58 madeof the same material and having the same shape as those of the movablemirrors 56 and 57 is provided on each of the surfaces of the substrates51 and 52 on the side opposite to the surface where the movable mirrors56 and 57 are formed. According to this structure, the bending momentcaused by the internal stresses of the movable mirrors 56 and 57 and theelectrodes 541 and 542 and acting on the substrates 51 and 52 isbalanced with the bending moment caused by the internal stresses of thedummy electrodes 59 and the anti-reflection films 58 and acting on thesubstrates 51 and 52. Thus, bends of the substrates 51 and 52 can bereduced. In addition, the substrates 51 and 52 have symmetric structure,which further reduces the bends of the substrates 51 and 52 andmaintains parallelism between the first movable mirror 56 and the secondmovable mirror 57. Accordingly, the resolution of the etalon 5A furtherincreases.

Modifications of Embodiments

The invention is not limited to the embodiments described herein butincludes modifications, improvements and the like of the embodimentswithout departing from the scope of the invention. For example, thefollowing changes may be made.

According to the respective embodiments, the gap varying unit in theappended claims is constituted by the electrostatic actuator 54.However, the gap varying unit may be an electromagnetic actuator 55shown in FIG. 8, for example. The electromagnetic actuator 55 has anelectromagnetic coil 551 to which current is supplied, and a permanentmagnet 552 which shifts toward the electromagnetic coil 551 by anelectromagnetic force. The electromagnetic coil 551 is disposed on thefirst electrode fixing surface 514A of the first substrate 51. Thepermanent magnet 552 is disposed on the second electrode fixing surface524A of the second substrate 52. The electromagnetic coil 551 and thepermanent magnet 552 are positioned so as to be opposed to each other.When current flows in the electromagnetic coil 551, the electromagneticcoil 551 and the permanent magnet 552 shift closer to each other by themagnetic flux given from the permanent magnet 551 and theelectromagnetic force produced by the interaction between the magneticflux and the current. Accordingly, the displacement units 511 and 522can shift relative to each other.

According to the respective embodiments, the linkage portions 513 and523 are formed by annular diaphragms. However, the first linkage portion513 may be constituted by beams which extend from the center of thefirst movable portion 512 in the etalon plan view as the symmetry centertoward positions of point symmetry. More specifically, as illustrated inthe plan view in FIG. 9 showing a modification of the etalon 5 in thefirst embodiment, the first linkage portion 513 is defined by fourthrough holes 50 provided outside the first movable portion 512 andpenetrating through the first movable portion 512 in the substratethickness direction. In this structure, the ring-shaped electrostaticactuator 54 is provided on the surface of the first movable portion 512on the side facing to the second substrate 52 at a position outside thefirst movable mirror 56.

According to the respective embodiments, the electrostatic actuator 54has a single-ring shape. However, the electrostatic actuator 54 may havea double-ring shape as illustrated in FIG. 10. More specifically, asillustrated in the plan view in FIG. 10 showing a modification of theetalon 5 in the first embodiment, the etalon 5 has a first electrostaticactuator 71 (gap varying unit) having a ring shape and disposed outsidethe first movable mirror 56, and a second electrostatic actuator 72 (gapvarying unit) having a C-ring shape and disposed outside the firstelectrostatic actuator 71. These first and second electrostaticactuators 71 and 72 are provided on each surface of the first movableportion 512 and the second movable portion 522 on the side facing toeach other.

An inside first electrode extension portion 711L extends from a part ofthe outer circumference of an inside first electrode 711 (electrodeprovided on the first substrate 51) of the first electrostatic actuator71 toward the upper left of the etalon 5 in the etalon plan view. Inaddition, an inside first electrode pad 711P is provided at the end ofthe inside first electrode extension portion 711L and connected with thevoltage control unit 6 (see FIG. 1). According to this structure,voltage is applied to the inside first electrode pad 711P from thevoltage control unit 6 (see FIG. 1) during operation of the firstelectrostatic actuator 71.

On the other hand, an outside first electrode extension portion 721Lextends from a part of the outer circumference of an outside firstelectrode 721 (electrode provided on the first substrate 51) of thesecond electrostatic actuator 72 toward the lower right of the etalon 5in the etalon plan view. In addition, an outside first electrode pad721P is provided at the end of the outside first electrode extensionportion 721L and connected with the voltage control unit 6 (see FIG. 1).According to this structure, voltage is applied to the outside firstelectrode pad 721P from the voltage control unit 6 (see FIG. 1) duringoperation of the second electrostatic actuator 72.

Second electrodes 712 and 722 (electrodes provided on the secondsubstrate 52) of the electrostatic actuators 71 and 72 are disposed soas to be opposed to the first electrodes 711 and 721. A second electrodeextension portion 712L extends from a part of the outer circumference ofthe inside second electrode 712 toward the upper right of the etalon 5in the etalon plan view in such a manner as to cross over the outsidesecond electrode 722. A second electrode pad 712P is provided at the endof the second electrode extension portion 712L and connected with thevoltage control unit 6 (see FIG. 1). According to this structure,voltage is applied to the second electrode pad 712P from the voltagecontrol unit 6 (see FIG. 1) during operation of the electrostaticactuators 71 and 72.

In this modification, applied voltage can be controlled for each of theelectrostatic actuators 71 and 72 by using the voltage control unit 6.Thus, more accurate gap setting can be realized.

According to this modification, the electrostatic actuators 71 and 72are disposed on the surfaces of the first movable portion 512 and thesecond movable portion 522 on the sides facing to each other. However,the electrostatic actuators 71 and 72 may be positioned on the surfacesof the first linkage portion 513 and the second linkage portion 523 onthe sides facing to each other.

While the modification of the first embodiment is shown in FIG. 10 as anexample, the modification may be incorporated in the etalon 5A in thesecond embodiment. In this case, the dummy electrode has a double-ringshape.

According to the respective embodiments, the substrates 51 and 52 havethe same shape. However, the thickness of the first substrate 51 may bemade smaller than the thickness of the second substrate 52 as in thecase of an etalon 5B show in FIG. 11. Alternatively, the thickness ofthe first substrate 51 may be made larger than the thickness of thesecond substrate 52.

According to the first embodiment, the first circular groove 514 isformed on the first substrate 51, and the third circular groove 524 isformed on the second substrate 52, so as to secure the gap G between themirrors and the gap between the electrodes. However, the first circulargroove 514 and the third circular groove 524 may be eliminated. In thiscase, each thickness of the bonding layers 53 between the substrates 51and 52 may be increased to secure the gap G between the mirrors and thegap between the electrodes. In this modification, the necessity ofperforming the steps for forming the first circular groove 514 and thethird circular groove 524 can be eliminated, which simplifies themanufacture process.

According to the second embodiment, the linkage portions 513 and 523 aredisposed at the centers in the thickness directions of the substrates 51and 52. However, the linkage portions 513 and 523 are not required to bepositioned at the centers.

According to the respective embodiments, the electrodes 541 and 542 areproduced prior to the formation of the movable mirrors 56 and 57 in themanufacture processes of the substrates 51 and 52. However, the movablemirrors 56 and 57 may be produced before the manufacture of theelectrodes 541 and 542.

According to the respective embodiments, the bonding surfaces 51A and52A are bonded via the bonding layers 53. However, the bonding surfaces51A and 52A may be bonded to each other by so-called cold activationbonding which activates the bonding surfaces 51A and 52A, overlaps theactivated bonding surfaces 51A and 52A with each other, and pressurizesthe overlapped surfaces 51A and 52A for bonding without forming thebonding layers 53, for example. The method for this purpose may bearbitrarily selected.

According to the respective embodiments, an optical module in theappended claims is constituted by the colorimetric sensor 3, and a lightanalyzer in the appended claims is constituted by the colorimeter 1including the colorimetric sensor 3. However, the optical module may bea gas sensor which introduces gas into the sensor and detects lightincluded in incident light and absorbed by the gas. In this case, thelight analyzer may be a gas detection device which analyzes anddetermines the gas introduced into the sensor by using the gas sensor.The light analyzer may be a spectral camera, a spectral analyzer or thelike including the optical module.

The optical module may have a structure which varies the intensities oflights having different wavelengths as time elapses whereby data istransmitted by lights of respective wavelengths. In this case, theetalon 5 included in the optical module divides light having aparticular wavelength and allows the light to be received by a lightreceiving unit for extraction of data transmitted by the light havingthe particular wavelength. The light analyzer equipped with this type ofdata extraction optical module can provide optical communication basedon data processing associated with lights having respective wavelengths.

What is claimed is:
 1. A wavelength variable interference filter,comprising: a first substrate; a second substrate that is disposed so asto be opposed to the first substrate; a first mirror that is disposedbetween the first substrate and the second substrate; a second mirrorthat is disposed between the first mirror and the second substrate; afirst electrode that is disposed between the first substrate and thesecond substrate; and a second electrode that is disposed between thefirst electrode and the second substrate, the first mirror beingdisplaced toward a second mirror side by applying a voltage between thefirst electrode and the second electrode, the second mirror beingdisplaced toward a first mirror side by applying the voltage between thefirst electrode and the second electrode.
 2. The wavelength variableinterference filter according to claim 1, the first substrate having afirst portion and a second portion, looking from a first substrate sideto the second substrate side, the first mirror overlapping to the firstportion.
 3. The wavelength variable interference filter according toclaim 2, the first portion being thicker than the second portion.
 4. Thewavelength variable interference filter according to claim 2, lookingfrom the first substrate side to the second substrate side, the secondmirror overlapping to the first portion.
 5. The wavelength variableinterference filter according to claim 2, looking from the firstsubstrate side to the second substrate side, the first electrodeoverlapping to the second portion.
 6. The wavelength variableinterference filter according to claim 2, the second substrate having athird portion and a fourth portion, looking from the first substrateside to the second substrate side, the second mirror overlapping to thethird portion.
 7. The wavelength variable interference filter accordingto claim 6, the third portion being thicker than the fourth portion. 8.A wavelength variable interference filter comprising: a first mirror; asecond mirror that is disposed so as to be opposed to the first mirror;and a gap varying unit that displaces the first mirror to a secondmirror side and the second mirror to a first mirror side.
 9. An opticalmodule comprising: the wavelength variable filter according to claim 1.10. A light analyzer comprising: the wavelength variable filteraccording to claim 1.